The structure of a tricarbonyliron derivative of Barbaralone

Abstract

One minor product of the reaction of Fe 2(CO) 9 in ether with impure bicyclo[2.6.0]deca-2,4,6-triene, in which the major impurity was cyclooctatetreane, is a derivative of barbaralone, tricyclo [3.3.1.0 2,8]nona-3,6-diene-9-one, I, in which the three membered ring has been opened at the 2.8 bond. The systematic name for the compounds is (2,3,4,8-η 4-bicyclo[3.2.2]-nona-3,6-diene-2,8-yl-9-one)tricarbonyliron. It is identical to the product which can be obtained by direct reaction of barbaralone with Fe 2(CO) 9 in ether. The most likely progenitor of the barbaralone moiety in the present instance in the C 8H 8 impurity, although there is no direct proof of this. Compound I crystallized from pentane at −5° in the triclinic system with unit cell dimensions a 7.476(2), b 11.912(4), c 6.606(2) Å, α 94.55(2)°, β 110.17(2)°, γ 92.38(3)°, V 549.0(3) Å 3 and Z 2. Space group P 1 . The structure was solved by Patterson and Fourier methods and refined to R 1 0.021 and R 2 0.031 with all nonhydrogen atoms treated anisotropically and the eight hydrogen atoms treated isotropically, using 1283 reflections having F 2 0 > 3 σ ( F 2 0). The coordination about the iron atom can be described as distorted octahedral if the η 3-allyl is considered to occupy two of the six positions. The three CO ligands are mutually cis. The allyl group is trans to two of them and FeC σ bond is trans to the third. The mean FeCO bond lengths is 1.795(5) Å, the FeC(allyl) distances are 2.137(3), 2.069(2) and 2.195(3) Å, and the FeC σ bond has a length of 2.110(2) Å. The broad geometrical features of the structure are quite at variance with the concept of a “homobutadiene complex”.